Waveguide cold noise source and temperature control method

Abstract

The application discloses a waveguide cold noise source and a temperature control method, and solves the problems of unstable output temperature of a waveguide cold noise source, easy leakage of liquid nitrogen and difficulty in replacing a matching load in the prior art. The waveguide cold noise source comprises a sealed liquid nitrogen container, a heat transfer structure, a waveguide mounting rack, a waveguide, a load and a temperature control structure. The waveguide mounting rack is fixedly connected with the liquid nitrogen container through the heat transfer structure. The waveguide is a hollow pipeline installed in a through groove of the waveguide mounting rack. The load is located in a waveguide cavity. The temperature control structure comprises a heating film, a temperature sensor and a PID controller which are located between the liquid nitrogen container and the waveguide mounting rack. The temperature sensor is distributedly installed in the waveguide and measures the physical temperature of the load and feeds back to the PID controller. The PID controller adjusts the heating film according to the physical temperature feedback of the load and controls the working temperature of the load. The device of the application adjusts the physical temperature of the load in an interval and avoids the problems of liquid nitrogen leakage, standing wave deterioration and spectrum expansion difficulty.

Description

Technical Field

[0001] This application relates to the field of noise measurement technology, and in particular to a waveguide cold noise source and a temperature control method. Background Technology

[0002] The noise figure of a radar receiver is one of its key technical specifications, and waveguide cold noise sources are commonly used in testing. A radiometer is a high-sensitivity receiver that receives the natural radiation of an object and is widely used in remote sensing. Waveguide cold noise sources are one of the main devices used in evaluating the measurement accuracy, linearity, stability, and sensitivity of radiometers.

[0003] Traditional waveguide cold noise sources use liquid nitrogen immersion matching loads, where one end of the matching load is placed in liquid nitrogen and the other end passes through a liquid nitrogen container with an opening in the side wall and is connected to the test port through an insulated waveguide. Dry gas is injected into the waveguide through small holes in the waveguide wall to prevent water vapor from condensing on the inner wall of the waveguide.

[0004] However, traditional waveguide cold noise sources have the following drawbacks. First, because the waveguide is directly immersed in liquid nitrogen, using the liquid nitrogen to provide cooling for the matched load, the physical temperature of the load cannot be adjusted. The noise source output temperature may vary with factors such as gas pressure, liquid level, and internal container pressure. Second, due to the structure where the matched load passes through the liquid nitrogen container, the long-term stability of the sealing structure at the perforation points is problematic. Since the temperature near the liquid nitrogen is -196 degrees Celsius, while the outside of the liquid nitrogen container is close to room temperature, differences in thermal expansion and contraction between different materials, vibration testing, and the lifespan of adhesives at low temperatures can all cause unpredictable liquid nitrogen leakage risks. Third, dry gas is injected into the waveguide through small holes in the rectangular waveguide wall to prevent water vapor condensation on the inner wall. However, any opening in the rectangular waveguide signal transmission path will generate unwanted standing waves and affect the noise test results. This problem becomes more prominent as the operating frequency increases. Because the size of the gas injection orifice is difficult to reduce proportionally with the waveguide size, the standing wave ratio (SWR) of traditional rectangular waveguide cold noise sources above 110 GHz is no longer sufficient for measurement requirements. Fourth, the matching load of traditional waveguide cold noise sources is permanently fixed to the liquid nitrogen container; any replacement will damage its sealing structure, resulting in high replacement costs. Therefore, there is an urgent need for a waveguide cold noise source that eliminates the risk of liquid nitrogen leakage, has a dry gas injection structure that does not affect the SWR, is easy to replace, and can be extended to higher frequency bands. Summary of the Invention

[0005] This application provides a waveguide cold noise source and a temperature control method, which solves the problems of unstable output temperature, easy liquid nitrogen leakage, and difficulty in replacing the matching load in the prior art.

[0006] This application embodiment also provides a waveguide cold noise source, comprising a sealed liquid nitrogen container, a heat transfer structure, a waveguide mounting bracket, a waveguide, a load, and a temperature control structure. The waveguide mounting bracket is fixedly connected to the liquid nitrogen container via the heat transfer structure. A through-channel is formed on the waveguide mounting bracket. The waveguide is a hollow pipe installed on the waveguide mounting bracket through the through-channel. Dry gas is injected from the end of the waveguide; the injection structure is not on the noise signal transmission path. The load is located within the waveguide cavity in the through-channel. The temperature control structure includes a heating film, temperature sensors, and a PID controller located between the liquid nitrogen container and the waveguide mounting bracket. The temperature sensors are distributed within the waveguide, measuring the physical temperature of the load and feeding it back to the PID controller. The PID controller adjusts the heating film based on the physical temperature feedback of the load to control the operating temperature of the load.

[0007] Preferably, the waveguide mounting bracket has multiple through slots, and multiple waveguides are respectively installed in the through slots.

[0008] Furthermore, the waveguide includes a first waveguide and a second waveguide. The first waveguide is located within the through-channel of the waveguide mounting bracket, and its internal cavity accommodates the load. Two second waveguides are respectively mounted on both sides of the first waveguide and are made of a low thermal conductivity material to reduce heat exchange between the first waveguide and components other than the waveguide mounting bracket.

[0009] Furthermore, the heating film consists of multiple sheets and covers different positions above the waveguide mounting bracket.

[0010] Furthermore, it also includes a gas guide tube and a solenoid valve. One end of the gas guide tube is connected to the waveguide end, and the other end is used to inject dry gas. The solenoid valve is used to draw dry gas and inject it into the waveguide.

[0011] More preferably, one end of the waveguide is connected to a gas duct and a solenoid valve is installed thereon, while the other end is a noise output port.

[0012] Preferably, the air duct is made of a material with low thermal conductivity.

[0013] Preferably, the liquid nitrogen container provides dry gas to the waveguide. A gas delivery pipe seals and connects the interior of the liquid nitrogen container to the interior of the waveguide. The connection point between the gas delivery pipe and the liquid nitrogen container is above a threshold height of the liquid nitrogen level.

[0014] Preferably, the gas delivery pipe is installed on the top wall of the liquid nitrogen container.

[0015] On the other hand, this application also provides a waveguide cold noise source temperature control method, using the waveguide cold noise source described in any of the above embodiments, comprising the following steps:

[0016] The temperature sensor measures the physical temperature of the load and feeds the physical temperature signal back to the PID controller.

[0017] A temperature threshold is set, and the PID controller determines the physical temperature of the load based on the temperature threshold.

[0018] The PID controller sends commands to the heating film to control the amount of heat generated by the heating film.

[0019] The above-described technical solutions adopted in the embodiments of this application can achieve the following beneficial effects:

[0020] The device described in this invention can adjust the physical temperature of the matching load within a certain range to keep its output temperature stable. It avoids the liquid nitrogen leakage hazard of traditional waveguide noise sources, solves the standing wave degradation problem and spread spectrum difficulties introduced by the dry gas injection method of traditional waveguide noise sources, and solves the problem of difficult maintenance and replacement of the matching load of traditional rectangular waveguide noise sources. Attached Figure Description

[0021] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0022] Figure 1 This is a structural diagram of an embodiment of a waveguide cold noise source according to this application;

[0023] Figure 2 This is a schematic diagram of an embodiment of the PID controller in this application;

[0024] Figure 3 This is a flowchart of an embodiment of a waveguide cold noise source temperature control method according to this application. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0026] The technical solutions provided by the various embodiments of this application are described in detail below with reference to the accompanying drawings.

[0027] Figure 1 This is a structural diagram of an embodiment of a waveguide cold noise source according to this application.

[0028] A waveguide cold noise source includes a sealed liquid nitrogen container 1, a heat transfer structure 2, a waveguide mounting bracket 3, a waveguide 4, and a load 5.

[0029] The waveguide mounting bracket is fixedly connected to the liquid nitrogen container via a heat transfer structure.

[0030] For example, a liquid nitrogen container with no side openings is used to provide cooling. Liquid nitrogen enters the container through the inlet 11 at the top and exits through the outlet 12. The liquid nitrogen concentrates at the bottom due to gravity. The cross-section of the container can be circular, rectangular, or square, etc., without further limitation. Pure copper or aluminum alloy is preferred. The bottom surface of the liquid nitrogen container with no side openings is a smooth metal surface.

[0031] The waveguide mounting bracket is connected to the outer bottom surface of the liquid nitrogen container through a heat transfer structure, thereby achieving temperature conduction and controlling the temperature of the waveguide.

[0032] The heat transfer structure is used to connect the liquid nitrogen container to the waveguide mounting bracket, providing cooling capacity for the waveguide and matching load. It also uses a heating film and PID controller to regulate the temperature of the waveguide and load within a certain range, ensuring that the output temperature remains stable over a long period of time.

[0033] The waveguide mounting bracket has a through-slot. The waveguide is a hollow tube that passes through the through-slot and is mounted on the waveguide mounting bracket.

[0034] Since a liquid nitrogen container can be used for multiple waveguides, in order to prevent waste, it is preferable that the waveguide mounting bracket has multiple through slots, and the multiple waveguides are respectively installed in the through slots.

[0035] For example, the waveguide is a rectangular waveguide, and a waveguide mounting bracket is used to mount the waveguide. A piece of metal, made of the same material as the liquid nitrogen container's base plate, has multiple rectangular through-channels machined onto it, the same size as or slightly larger than the outer wall of the rectangular waveguide. After applying thermal grease to the inside of the through-channels, multiple rectangular waveguides can be mounted. The waveguide mounting bracket also includes a clamping base plate, which is used to secure multiple matched loads, achieving a firm installation and good thermal conductivity. The base plate is made of a low thermal conductivity material to reduce heat exchange between the waveguide and the external environment.

[0036] The load is located in the waveguide cavity within the waveguide mounting bracket groove.

[0037] The waveguide includes a first waveguide 41 and a second waveguide 42. The first waveguide is located within the through-slot of the waveguide mounting bracket, and its internal cavity accommodates the load.

[0038] For example, the first waveguide is a rectangular waveguide, installed in the through groove of the waveguide mounting bracket.

[0039] The two second waveguides are respectively mounted on both sides of the first waveguide and are made of low thermal conductivity material to reduce heat exchange between the first waveguide and components other than the waveguide mounting bracket.

[0040] For example, the second waveguide is an adiabatic straight waveguide, and one end of each of the two second waveguides is fixedly connected to the two ends of the first waveguide.

[0041] Dry gas is injected into the waveguide from its end via a gas delivery pipe 6 and a solenoid valve 7 to prevent water vapor condensation on the inner wall of the waveguide. One end of the gas delivery pipe is connected to the waveguide end, and the other end is connected to a nitrogen cylinder. The solenoid valve is used to extract nitrogen gas and inject it into the waveguide.

[0042] Dry gas is injected into the waveguide end, and the injection structure is not in the transmission path of the noise signal, thus avoiding the problems of standing wave degradation and spread spectrum difficulties.

[0043] The air duct is an adiabatic transition waveguide, usually made of low thermal conductivity metals such as stainless steel with gold plating on the inner wall. It can reduce heat exchange between the second waveguide and the structure it is connected to.

[0044] The liquid nitrogen container can also be used as a nitrogen cylinder to provide dry gas to the waveguide. The gas delivery tube is sealed and connects the interior of the liquid nitrogen container and the interior of the waveguide. The connection point between the gas delivery tube and the liquid nitrogen container is above a threshold height of the liquid nitrogen level.

[0045] The existing waveguide technology requires it to extend into liquid nitrogen to transfer heat and achieve a cooling effect. However, the waveguide is not internally connected to the liquid nitrogen. Inserting the waveguide through an opening in the side wall of the liquid nitrogen container requires immersing it in the liquid, which easily leads to liquid nitrogen leakage. In contrast, the gas vent is connected to the inside of the liquid nitrogen container, only requiring the extraction of nitrogen. Therefore, the height of the gas vent needs to be higher than the liquid nitrogen level threshold, i.e., the maximum height. To prevent vibration from causing the liquid nitrogen level to exceed the height of the gas vent opening under uncertain circumstances, thus leading to liquid nitrogen leakage, it is preferable that the gas vent opening is installed on the top wall of the liquid nitrogen container.

[0046] Since the liquid nitrogen container itself needs to be continuously injected with liquid nitrogen from the top injection port and discharged from the exhaust port, it is preferable to directly connect the exhaust port of the liquid nitrogen container to the lower waveguide end through the gas guide pipe, without the need to use an additional nitrogen tank.

[0047] One end of the waveguide is connected to the air duct and a solenoid valve is installed thereon, while the other end is a noise output port.

[0048] For example, the other ends of the two second waveguides are connected to a nitrogen cylinder and the receiver under test, respectively. The end connected to the nitrogen cylinder is used for injecting dry gas, while the end connected to the receiver under test is the noise output end. The second waveguide is made of a low thermal conductivity metal such as stainless steel with a gold-plated inner wall, which can reduce heat exchange between the end first waveguide and the connected structure. Therefore, preferably, the gas duct, i.e., the second waveguide, is made of a low thermal conductivity material.

[0049] The device in this application also includes a temperature control structure. The temperature control structure includes a heating film 8, a temperature sensor 9, and a PID controller 10 located between the liquid nitrogen container and the waveguide mounting bracket (e.g., [missing information]). Figure 2 (As shown).

[0050] Figure 2 This is a schematic diagram of an embodiment of the PID controller in this application.

[0051] The temperature sensors are distributed within the waveguide and measure the physical temperature of the load, feeding it back to the PID controller 10. The PID controller adjusts the heating film based on the load's physical temperature feedback to control the load's operating temperature.

[0052] The heating film can be installed on the outer bottom surface of the liquid nitrogen container.

[0053] For example, a heating film is installed on the bottom surface of the liquid nitrogen container. By combining liquid nitrogen refrigeration with electric heating technology, the physical temperature can be varied within a range greater than 200K and across the ambient temperature range, thus achieving temperature regulation for the matched load.

[0054] Specifically, the heating film is installed close to the bottom surface of the liquid nitrogen container, with an area roughly equal to the bottom surface. The function of the heating film is to raise the physical temperature of the homogenizer and regulate the temperature within a certain range. The heating film is connected to a PID controller, which determines the required heating power to be applied to the heating film based on the temperature sensor readings.

[0055] The heating film can also be installed between the heat transfer structure and the waveguide mounting bracket.

[0056] For example, a heating film is installed on the mesh plane of the heat transfer structure facing the waveguide mounting bracket.

[0057] Since the function of the heating film is to provide a stable temperature for the waveguide, and the heating film is installed below the liquid nitrogen container, which has a low temperature, the heating film requires more power and is not the optimal choice in terms of energy loss. Therefore, it is preferable that the heating film is located between the heat transfer structure and the waveguide mounting bracket.

[0058] The heating film can be a single piece covering the waveguide mounting frame, or multiple heating films can be covering different positions above the waveguide mounting frame.

[0059] For example, since the waveguide is located in the through slot of the waveguide mounting frame and there are multiple through slots, using the same heating film to cover the waveguide mounting frame cannot meet the requirement of uniform heating of all directions of the waveguide. Therefore, it is preferable to cover multiple heating films at different positions above the waveguide mounting frame.

[0060] For example, the PID controller adjusts the heating film based on the temperature sensor's measurement results, ensuring a long-term stable operating temperature for the matched load with injected dry gas. This avoids the problem of the output temperature of traditional rectangular waveguide cold noise sources varying with gas pressure, liquid level, and internal container pressure.

[0061] For example, the load is a double-wedge absorber connected to a temperature control structure, with dry nitrogen gas injected into the waveguide end. One end is connected to the liquid nitrogen container via a second waveguide, a heat pipe, and the other end is connected to the test interface via the second waveguide. Since the dry gas injection structure is not on the noise signal transmission path, unwanted standing wave reflections are not generated. Multiple temperature sensors are distributedly installed within the first waveguide to measure the physical temperature of the load and feed it back to the PID controller. Based on the temperature sensor measurements, the PID controller adjusts the heating film to ensure long-term stability of the load's operating temperature, avoiding the problem of output temperature variations caused by gas pressure, liquid level, and internal container pressure in traditional rectangular waveguide cold noise sources.

[0062] Alternatively, the solenoid valve can be connected to the nitrogen cylinder, and the nitrogen supply can also be adjusted by a PID controller; no further limitations are made here.

[0063] Figure 3 This is a flowchart of an embodiment of a waveguide cold noise source temperature control method according to this application.

[0064] A method for controlling the temperature of a waveguide cold noise source, using the waveguide cold noise source described in any of the above embodiments, includes the following steps:

[0065] Step 101: The temperature sensor measures the physical temperature of the load and feeds the physical temperature signal back to the PID controller.

[0066] Multiple temperature sensors are installed inside the first waveguide to measure the physical temperature of the load and feed the measurement results back to the PID controller.

[0067] Step 102: Set a temperature threshold, and the PID controller will determine the physical temperature of the load based on the temperature threshold.

[0068] A temperature threshold is set, and the PID controller compares the measured physical temperature with the temperature threshold to determine the command to be issued to the heating film based on the comparison result.

[0069] Step 103: The PID controller sends instructions to the heating film to control the amount of heat generated by the heating film.

[0070] If the measured physical temperature is below the temperature threshold, the PID controller sends a command to increase the temperature. If the measured physical temperature is above the threshold, the PID controller sends a command to decrease the temperature.

[0071] The above description is merely an embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of this application should be included within the scope of the claims of this application.

Claims

1. A waveguide cold noise source, characterized in that, Includes a sealed liquid nitrogen container, heat transfer structure, waveguide mounting bracket, waveguide, load, and temperature control structure; The waveguide mounting bracket is fixedly connected to the liquid nitrogen container via a heat transfer structure. The waveguide mounting bracket has a through groove. The waveguide is a hollow pipe installed on a waveguide mounting frame through a through-channel; dry gas is injected from the end of the waveguide, and the injection structure is not on the transmission path of the noise signal; The load is located in the waveguide cavity within the through-channel; The temperature control structure includes a heating film, a temperature sensor, and a PID controller located between the liquid nitrogen container and the waveguide mounting frame. The temperature sensors are distributed and installed inside the waveguide to measure the physical temperature of the load and feed it back to the PID controller. The PID controller adjusts the heating film based on the physical temperature feedback of the load to control the operating temperature of the load.

2. The waveguide cold noise source according to claim 1, characterized in that, The waveguide mounting bracket has multiple through slots, and multiple waveguides are installed in the through slots respectively.

3. The waveguide cold noise source according to claim 1, characterized in that, The waveguide includes a first waveguide and a second waveguide; The first waveguide is located in the through groove of the waveguide mounting bracket, and its internal cavity accommodates the load; The two second waveguides are respectively mounted on both sides of the first waveguide and are made of low thermal conductivity material to reduce heat exchange between the first waveguide and components other than the waveguide mounting bracket.

4. The waveguide cold noise source according to claim 1, characterized in that, The heating film consists of multiple sheets, which cover different positions above the waveguide mounting bracket.

5. The waveguide cold noise source according to claim 1, characterized in that, It also includes an air duct and a solenoid valve; One end of the gas duct is connected to the waveguide end, and the other end is injected with dry gas; The solenoid valve is used to draw dry gas and inject it into the waveguide.

6. The waveguide cold noise source according to claim 5, characterized in that, One end of the waveguide is connected to the air duct and a solenoid valve is installed thereon, while the other end is a noise output port.

7. The waveguide cold noise source according to claim 5, characterized in that, The air duct is made of a material with low thermal conductivity.

8. The waveguide cold noise source according to claim 5, characterized in that, The liquid nitrogen container provides dry gas for the waveguide; The gas delivery tube is sealed to connect the inside of the liquid nitrogen container and the inside of the waveguide; The gas delivery pipe is connected to the liquid nitrogen container at a height higher than the liquid nitrogen surface height threshold.

9. The waveguide cold noise source according to claim 8, characterized in that, The gas delivery pipe is installed on the top wall of the liquid nitrogen container.

10. A method for controlling the temperature of a waveguide cold noise source, characterized in that, Using the waveguide cold noise source according to any one of claims 1-9, the steps are as follows: The temperature sensor measures the physical temperature of the load and feeds the physical temperature signal back to the PID controller; Set a temperature threshold, and the PID controller will determine the physical temperature of the load based on the temperature threshold. The PID controller sends commands to the heating film to control the amount of heat generated by the heating film.

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